Field
Disclosed herein are systems and methods for measuring perfusion and blood flow. More particularly, a system is disclosed using laser speckle imaging in a transmission geometry to measure perfusion and blood flow.
Description of the Related Art
Many situations exist where the perfusion of tissues with blood is correlated to the health and/or physical state of an individual. For example, during traumatic injuries, a potentially worsening prognosis is indicated by transient peripheral limb ischemia (e.g., decreased blood flow to peripheral limb tissues). In this case, blood is preferentially collected within the vital organs of the body. A clinician can typically only visually recognize signs of this event by observing the onset of cyanosis. However, cyanosis only becomes visible at blood oxygenation levels far below normal physiologic levels (˜<80%). As such, devices and methods for quantitatively measuring and reporting the degree of perfusion and the strength of blood flow within peripheral limbs before the onset of cyanosis would aid clinicians in treating patients in critical condition earlier than would be possible based on visual assessment. In addition, peripheral limb perfusion has been demonstrated as an indicator of the onset of general and epidural anesthesia, infectious outcomes in neonates and infants, and restriction and/or restoration of blood flow during surgical procedures. Peripheral perfusion measurements may also provide diagnostic or prognostic information in individuals with peripheral vascular disorders.
Pulse oximetry is a common method for clinical assessment of pulse rate, blood oxygenation, and perfusion. This method relies on the changes in light absorption resulting from the pulsatile flow of arterial blood. Currently, pulse oximeters do not measure perfusion directly, but rely instead on other measured parameters that may be correlated with perfusion. They also require a pulsatile beat to determine these parameters. As a result, the functionality of pulse oximeters to measure perfusion is compromised under conditions such as ischemia, low cardiac output, or the use of extracorporeal means to provide blood flow. These conditions can result in pulse oximeters giving erroneous information, or no information at all. Thus pulse oximeters fail to deliver information that could be integral to proactively treating patients with potentially decreased blood flow.
Another method for assessment of perfusion uses a laser Doppler flowmeter. Laser Doppler flowmeters only interrogate tissue ˜1 mm deep with respect to the surface of the tissue. Such a small depth of interrogation may result in sampling only superficial blood vessels when used on human patients. This would limit the data acquired from larger arteries, arterioles, veins, and venules, which may provide more valuable perfusion information.
Further, conventional laser Doppler flowmeters used for point measurement on patients utilize an optical fiber to transfer light to and from the probe. Movements of this optical fiber result in erroneous changes in reported perfusion values. As such, patient movement can have significant deleterious effects on acquired perfusion data.
Additionally, typical laser Doppler flowmeters cost tens of thousands of dollars. This high cost significantly limits the availability of such devices to a fairly limited number of applications and precludes using such devices in the majority of emergency rooms, surgical suits, ambulances, or disaster or battlefield triage sites, etc.